21097 has 6 divisors (see below), whose sum is σ = 22718. Its totient is φ = 19584.

The previous prime is 21089. The next prime is 21101. The reversal of 21097 is 79012.

It can be written as a sum of positive squares in 3 ways, for example, as 9216 + 11881 = 96^2 + 109^2 .

It is not a de Polignac number, because 21097 - 2³ = 21089 is a prime.

It is a Duffinian number.

It is not an unprimeable number, because it can be changed into a prime (21017) by changing a digit.

It is a pernicious number, because its binary representation contains a prime number (7) of ones.

It is a polite number, since it can be written in 5 ways as a sum of consecutive naturals, for example, 253 + ... + 325.

2²¹⁰⁹⁷ is an apocalyptic number.

21097 is the 73-rd decagonal number.

It is an amenable number.

21097 is a deficient number, since it is larger than the sum of its proper divisors (1621).

21097 is an equidigital number, since it uses as much as digits as its factorization.

21097 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 107 (or 90 counting only the distinct ones).

The product of its (nonzero) digits is 126, while the sum is 19.

The square root of 21097 is about 145.2480636704. The cubic root of 21097 is about 27.6316552013.

It can be divided in two parts, 2109 and 7, that added together give a square (2116 = 46²).

The spelling of 21097 in words is "twenty-one thousand, ninety-seven".